Electric-railway system



C. LE G. FORTESCUE.

ELECTRIC RAILWAY SYSTEM.

APPLICATION FILED M'AR. 7. 1916.

15304295. Patented M&y*2o,1919.

l f Il f 21 lwnNEssEs: i INVENTOR UNITED' sTATEs PATENT CEEICE.

CHARLES LE G. FoRTEsCUE, or PITTSBURGH, PENNSYLVANIA, -A'ssI-GrNo-R To WEST- INGI-IOUSE ELECTRIC AND MANUFACTURING COMPANY, A CORPORATION 0F PENNSYLVANIA.

ELECTRIC-RAILWAY SYSTEM.

Patented May 2o, 1919.

Application fnea March 7, 191e. serial No. 82,593.'

To all whom it may concern.'

Be it known that I, CHARLES LE G. FCR- TEsQUE, a subject of the King of Great Britain, and a resident of Pittsburgh, Pennsylvania, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Electric -Railway Systems, of which the following is a specification.

My invention relates to electric railway systems and especially to those that employ electric signaling devices and in which the track rails are utilized as return paths or conductors for the propulsion currents as well as paths for the signaling currents.

More particularly, my invention relates to electric railways of the above-indicated character in which the trolley conductors and the track rails are inductively interlinked with one another in order to minimize the inductive disturbances that may be impressed upon adjacent electrical circuits, such as intelligence-transmission circuits.

If ythe return flow of the trolley or propulsion currents of an electric railway system is confined to the track rails in preference to ground or earth return, inductive disturbances which arise from the power `currents tiowing in the railway system and are imposed upon any adjacent intelligencetransmission circuit may be greatlyv minimized. To accomplish this, it is proposed to insert series transformers at spaced intervals in they railway system, the primary windings of the transformers lbeing connected across insulating joints and in seriescircuit relationship with the trolley conductors, and the secondary windings being connected at corresponding points in the track and across insulating joints that divide the track into a plurality of rail sections which are utilized as the block-sections for .the

electric signaling system. By this means,

electromotive forces are impressed at intervals upon the track, thereby compensating for its high impedance which is occasioned The insulated block-sections formed by theiinsertion of the insulating joints in the track, as mentioned above, constitute local circuits for the signaling apparatus, and, to this end,the blocks should be insulated from one another as regards'v the signaling currents. At the same time, the blocks should be electrically continuous as regards-the propulsion currents, inasmuch as the tracks are employed as the return path for the propulsion currents. Heretofore, impedance bonds comprising inductive windings wound upon m'agnetizable core members and having their terminals connected to the two rails of a block section and their mid-points utilized for interconnecting adjacent block 'sections have been employed for limiting the flow of the signaling currents between adj acent block sections. However, the inductive reactance offered to the flow of the signaling currents by such impedance bonds is not sufficient to insure against the flow of leakage signaling currents between adjacent block sections. Such leakage currents frequently interfere with the proper operation of the signaling apparatus of the separate block sections whereby the signaling devices will sometimes indicate traflic conditions other than those that actually obtain on the associated section.

Again, .signaling currentsy are difficult to confine to their respective' block sections when a-railway installation comprises a plurality of parallel tracksv which are bonded together to provide a low-impedance path for the return flow of the propulsion currents, as mentioned above. When a rail of a block section or track circuit breaks, the leakage area alforded the broken rail, by reason of the proximity of corresponding block sections of the other tracks electrically bonded thereto, is frequently suthcient to permit the signaling devices to operate as though normal conditions vobtained upon the block section having the broken rail.` j' In this instance, it is essential that, when a j approaching train by the signaling apparatus. Another difficulty which has been prevalent in previous installations is the frequent operation' of signaling apparatus when no signaling current is intended to flow. rlhis results from the unequal resistance or inductance of the two rails of the track, this inequality giving rise to a potential difference between the two rails which will, of course, operate the signaling apparatus unless this apparatus is adjusted for operation with one frequency only. Since this latter provision'is quiten expensive, the signaling apparatus usually found on the standard American railway systems is liable to be operated by currents of a frequency otherthan the signaling-current frequency. In order to prevent this existence of a potential difference between the two rails of the track, means must be provided which establishes a short-circuit path between the two rails, that is, a path having substantially no impedance.

One object of my invention, therefore, is to provide means whereby the existence of such an undesirable potential difference of the wrong frequency may be prevented. I, therefore, provide means which are substantially resonant to currents of the desired frequency and which constitute a shortcircuit path Ibetween the two rails of the track. In this way, no potential difference exists and the tendency for the signaling apparatus to operateon other than desirable frequency potential is eliminated.

An object of my presentinvention is to incorporate means in a railway system whereby the tracks and the trolley conductors may be inductively interlinked with one another and, at the same time, the block sections will be electrically isolated from one another under all circumstances, the block sections, however, being electrically continuous as regards alternating currents having the frequency of the propulsion currents in order that the return flow of the propulsion currents may be confined to conductors, such as the rails comprising the tracks, that are in close proximity to the trolley conductors.

Another object of my 'invention is to provide means, in an electric railway system, whereby theseveral parallel tracks may be electrically bonded to one another to provide a path of very low impedance for the return flow of the propulsion currents and, at the same time, insure that the blocksections of the several tracks will be electrically isolated from :one another in order that the separate signaling devices may indicate, with accuracy, the conditions obtaining upon the severaltrack circuits. Underthese circumstances, and in view of the foregoing description, `it will be observed that the several tracks are inductively inis a representation illustrating an electrical.

equivalent of the transforming device of Fig. 2.

Referring to Fig. l, a source of alternating-current supply l, shown as a singlephase alternator, has one of its terminals connected to trolley conductors 2 and 3 and the other terminal connected to ground. The rails 5 and l are associated, respectively, with the aforementioned trolley conductors'. At spaced intervals, series transformers 6 are placed, one only of which is shown, to inductively interlink the trolley conductors and the tracks with one another for impressing electromotive forces at intervals in the tracks to compensate for their inherently high impedance. Thetransformer 6 comprises a primary winding 7 which is connected in series circuit with the trolley conductor 2 and a primary winding 8 which is connected in series circuit with the ltrolley conductor 3, a single secondary winding 9 being connected to the track rails 4 and 5, as will be hereinafter disclosed. The rails of the tracks l and 5 are more or less in cont-act with the earth, as is usual in all railway systems and, for this reason, theI secondary winding 9 of the transformer 6 is employed in order that the return flow of the propulsion currents may be confined to the tracks -l and in preference to the earth.

The rails comprising the tracks l and 5 are divided into a plurality of sections by means of insulating joints 10 which are placed therein at intervals corresponding to the insertion of the'primary windings 7 and S in the trolley conductors 2 and 3. The insulating joints l0 divide each track into a plurality of block sections ll, ila which are utilized as local circuits comprising the signa-ling system. The yblock section l1a is connected through a track transformer l2 to a signaling circuit 13 that supplies power to a relay 22 that operates a signaling device lit. Since the block sections ll, 11a are insulated from one another, as regards alternating currents having the frequency of the signaling. currents, transformers 15 servefto interconnect the block sections toone another in order to provide a return path of low impedance for the propulsion currents. The transformers l5 are disposed on both sides of each insulating joint 10 and their windings are connected, as will be hereinafter explained, to the secondary windings 9 of the transformer 6 and to the rails of the tracks in order to provide a path for the propulsion currents through the secondary windings 9 of the series transformers.

The transformer 15a comprises a primary winding 16 and a secondary winding 17, the latter of which is comiected in closed circuit 4with a condensive reactance element 18. One terminal of the primary winding 16 is electrically connected to a rail of the associated track 4, and the other terminal is connected to a common conductor 19a which represents an extension of one terminal of the secondary winding 9 of the transformer 6. The transformers 15 and 152L are employed to provide paths of low impedance for alternating currents having the frequency of the propulsion currents, while, at the same time, they substantially preclude the flow' therethrough of alternating currents having the frequency of the signaling currents. To this end, the windings 16 and 17 0f the transformer 15a are provided with means for establishing a leakage reactance therebetween which is an equivalent of inserting an inductive reactance element in the circuit. The capacity of the condenser 18 is so selected that the primary winding 16, which is subject to the leakagereactance between it and the secondary winding 17 and to the condensive reactance of the element 18 constitutes a series resonant circuit for alternating currents having the frequency of the propulsion currents. It will, therefore, be apparent that the propulsion currents may traverse the winding 16 of the transformer 15a and the corresponding windings of the like transformers without being offered any substantial impedance to their flow, while, at the same time, the signaling currents, having a frequency which differs from that of the propulsion currents, will be offered a substantially high impedance, since the winding 16 and the other windings corresponding thereto constitute paths tuned to the frequencyl of the propulsion currents only.

As explained above, a track comprising a single rail, or a pair 0f rails, has considerable impedance and, inasmuch as the two tracks 4 and 5 are disposedadjacent to each other, it is desirable to interconnect them in such a manner as to lower the impedance of the path for the return flow of the trolley currents. At the same time, it is desirable to minimize the inductive disturbances upon an intelligence-transmission circuit 20 shown as a telephone circuit which is sub` ject to the inductive disturbances arising from the currents flowing in the railwayl system. To this end. the tracks 4 and 5 are electrically connected to each other by means of the transformers such as 15, 15, 15b, etc., and the conductors 19, 19a, and the common secondary winding 9 of the transformer 6. It will be noted that each rail of they track circuits 4 and 5 is provided with two transformers as 15 and 15a which are associated with each insulating joint'lO. kBy means of such primary windings as thewinding 16, the rails of the tracks aremade electrically continuous through the secondarywinding 9 ofthe series transformer 6 only to alternating currents having the frequency of the propulsion currents. c

Under normal conditions of operation, the

signaling currents How in a local circuitV such as that formed by the track section 11a, a secondary winding 21 o-fv thetransformer 12 and a relay device 22 which is associated with the signaling device 14. lVhen the circuit is thus completed, the signaling device 14 indicates that the block section 11a yis open. When a train 23 bridges the rails of the track section 11a, the signaling currents are shunted from the relay 22, and thesignaling device 14 indicates that a train occupies the block section 11a. The propulsion currents from the train 23 return to the generator 1 through the block section 11a, the transformers 152l and 15b, the conductor 19a, the secondary winding 9 of the transformer 6, the conductor 19, the primary windings of the transformers 15, and the tracks 4 and 5, the latter being connected in parallel relationship to constitute a common conductor of low impedance. The signaling currents are confined to their respective track sec'- tions, inasmuch as the windings such as the winding 16 of the transformervla, offer high impedance to the flow of alternating currents having the frequency ofthe signaling currents. In consequence, the signaling currents are precluded from flowing between adjacent track sections and, therefore, the signaling device 14 is influenced only when the proper conditions obtainupon the block sections which the signals are severally designed to protect.

If one of the rails comprising the block section 11"L breaks, it is important that the signaling circuit of the relay 22 be entirely interrupted in order that the signaling device 14 may indicate danger. Since each track sec-' tion of either of the tracks 4 and 5 is paral# leled by a corresponding track section of the other track, there is danger that the leakage currents flowing between the two portions of the broken rail and from the adjacent track sections of the same track and the other tracks will'be sufficient to energize the sig-r f rail exists in the block section 11a. Topreclude the `flow 'of sufficient leakage current to interfere with the operation of the signal 14,

the transformer-S15 15a etc. are inserted'on trically isolated as regards the signaling currents, while, at the same time, it is connected to the other track sections as regards the propulsion currents. At the same'time,

the tracks are inductively interlinked with the trolley conductors in order to confine the' return flow of the propulsion currents to the tracks in preference to the earth so as to minimize the inductive disturbances that may be impressed upon the intelligencetransmission conducto-r 20.

In commercial installations, it may be necessary7 to compensate for the lirregular spacing of the intelligence-transmission conductor 20 relative to the railway system. For this reason, the `secondary windings@ of the transformers 6 are provided with a pluralityT of taps 24 by means'of which the ratios of the turns of the primary and secondary windings -may be regulated so as to force certain currents to iiow through the earth as a return circuit.

While I have shown the transformers 15, 151 as being the most desirable means for providing series resonant circuits which are tuned to the frequency only of the propulsion currents, other devices may be'employed in preference to these transformers for securing these results, it being understood that the transformers are utilized to illustrate a preferred means only for securing resonant conditions in a circuit traversed by currents of high values.

The construction of the transformers 15, 15, etc., is more clearly illustrated in Fig. 2 in which a rectangular magnetizable core member 25 constituting a closed magnetic circuit is furnished with a coil 26 which represents the primary winding 16 of Fig. 1.

The coil 26 surrounds the core leg 27, and the secondary winding 17 of Fig. 1 is represented by a coil 28 which surrounds a core leg 29 of the core member 25. vThe coil 28 is connected in closed circuit with a condenser 30. Magnetizable members 31 and 32 are positioned adjacent to the core legs 27 and 29, respectively, and are spaced therefrom by adjustable air gaps 33. It will be noted that the magnetizable members 31 and 32 bridgethose legs only of the core member 25 which lare provided with current-carrying coils. Inasmuch as the secondary windling 28 introduces a capacity reactance in the circuit comprising the primary winding 26, the internal 'reactance of the transformer, due to tlie magnetic leakage flux traversing the magnetic shunts 31 and 32, must be so proportioned as to annul the capacity reactance in order to establish series resonant conditions in` the circuit comprising the winding 26 for alternating currents having the frequency of the propulsion currents. To this end, the magnetizable core members 31 and 32 are provided to secure .magnetic leakage paths between the primary winding 26 and the secondary winding 2S. adjusting the positions of the members 31 and 32, series resonant conditions for alternating currents of the frequency of the propulsion currents are established in the circuit comprising the primary winding 26.

The diagrammatic circuit of Fig. 3 rcpresents an electrical equivalent of the transformer of Fig. 2 and constitutes a `condensive reactance element 311 connected in series relationship with a variable inductive reactance element 35 which is supplied with. a movable corevmember 36. By adjusting the position of the core member the reactance arising from the element may be exactly equal and opposite to the reactance arising Yfrom the element 34- when alternating currents of the frequency of the propulsion currents are impressed thereupon'.

While I have shown and described one embodiment of my invention, it will be understood that many modifications may be made therein without departing from the spirit and scope of the appended claims.

I claim as my invention:

1. In a railway system subjected to the flow of alternating currents of at least two frequencies, the combination with a trolley and a track comprising rails, of a series transformer inductively interlinking said trolley conductor and said track with each other, and means connected between each rail and said series transformer to permit currents of .one frequency only to flow through said series transformer and, at the same time, to prevent lthe existence of a potential difference of said frequency between said rails.

2. In a railway system subjected to the flow of alternating currents of at least two frequencies, the combination with a trolley and a track comprising rails, said track being sectionalized by insulating bonds, of a series transformer bridging said bonds and inductively interlinking said trolley conductor and said track, and means connected between each of said rails and said series transformer to permit the flow through said transformer of a current of one of said frequencies only, and, at the same time, to prevent the existence of a potential difference of said frequency between said rails.

3. In a railway system adapted to operate with alternating propulsion current of one frequency, the combination with a trolley conductor and an insulating-bond-sectionalized track comprising a plurality of signaling block sections adapted to operate with alternating signaling current of another frequency, of spaced transformers having their primary windings connected in series with said conductor and their secondary windings bridging said insulating bonds, and means connected between each of said rails and said secondary windings to permit the flow through said secondary windings of currents of said propulsion frequency only and, at the same time, to prevent the existence of a potential difference of said frequency between the rails of each of said block sections. i. In a railway system adapted to operate with alternating propulsion current of one frequency, the combination with a trolley conductor and an insulating-bond-sectionalized track comprising a plurality of signaling block sections adapted to operate with alternating signaling current of another frequency, of spaced transformers having their primary windings connected in series with said conductor and their secondary windings bridging said insulating bonds, and resonant circuits connected between each of the rails of said tracks and said secondary windings and tuned to the frequency of the propulsion current, whereby said track and said secondary winding constitute a pathof low impedance for currents having the frequency of the propulsion currents only, and whereby the existence of a potential difference of the propulsion-current frequency between the rails of said signaling section is prevented.

5. An electric railway system comprising a trolley conductor, a track comprising two rails divided into a plurality of insulated track sections, series transformers for inductively interlinking the trolley and track to each other' an d for connecting said track sections in series relationship with one another, and resonant circuits inserted between said transformers and each of the rails of said track sections to permit the flow of alternatingcurrents of a selected frequency only through successive track sections without encountering substantial impedance and to prevent the existence of a potential difference of said selected frequency between the rails of said track sections.

6. An electric railway system comprising a plurality of trolley conductors, a plurality of tracks each of which is divided into a plurality of insulated block sections, series transformers for inductively interlinking the trolley conductors and the tracks to one another,

each series transformer comprising primary windings that are severally connected 1n circuit with said trolley conductors and a secondary winding, and series resonant circuits connected between each of the rails and said secondary winding and tuned to the frequency of the propulsion currents only for connecting said secondary winding to each of said tracks whereby the existence of a potential difference of the frequency of said propulsion current is prevented.

In testimony whereof, I have hereunto subscribed my name this 29th day of Feb., 1916.

CHARLES LE Gr. FORTESCUE.

Copies of this patent may be obtained for ve cents each, by addressing the Commissioner of Patents, Washington, D. C. 

